DE3138084C2 - Concealed arc welding process for low carbon steel - Google Patents

Abstract

The invention relates to a concealed arc welding process, in particular a submerged arc welding process for very low-carbon steel for the production of line pipes with high strength and toughness. A welding wire with a C content of 0.18 to 0.55% is used and Ti and / or B are added to the welding wire and / or the flux so that both Ti and B are present in the weld metal. The welded steel has a C content of 0.005 to 0.06%.

Description

The invention relates to a covert arc welding process for very low carbon steel, in particular for the production of line pipes according to the preamble of claim 1.

I line pipes have high strength, high toughness, and good properties, especially at low temperatures.

Legal applications. An example of a hidden arc welding process is the so-called submerged powder

■ i 30 welding processes (submerged arc welding process).

H In the development of steels suitable for use in conduit pipes in cold climates

ή. is achieved by lowering the carbon content of low-alloy, high-strength steels and in particular

] | by lowering the carbon content of such steels to such a low level that the steels

Il have good weldability and low-temperature toughness, a significant advance has been achieved.

I; 35 With advances in controlled rolling processes, various low-carbon steels have been introduced

JJf a carbon content of not more than 0.06% available, while the carbon content is more common

I steels is around 0.1%.

; | Line pipes are made from high-strength, low-alloy steels by concealed arc welding

% produced, with a welding flux with an addition of Ti to improve the low-temperature toughness

* 40 and B and a welding wire with one of the following compositions are used together.

t'i det. The welding wires have the following compositions (data in weight percentages)

K cent):

Table I. C. Si Mn Mon <0.15
<0.17
0.10-0.18
0.10-0.18 0.05-0.25
<0.05
<0.05
0.05-0.30 1.30-1.80
1.80-2.20
1.70-2.40
1.75-2.25 #
#
0.45-0.65 JISSAW32
J1SSAW41
50 AWS Standard EA3
AWS Standard EH14

Annotation:

JlS = Japanese Industrial Standard.

SAW = Submerged Arc Welding ⁵⁵ AWS = American Welding Socieiy.

# = Mo and / or Ni or the like, in addition to the JIS components.

In the manufacture of a pipe from any of the above steels, various processes are used, for example the UOE process (U-ing and O-ing expander, U- and O-expansion process), the spiral

bo seam tube production and the roll bending process.

Usually, a low-alloy, low-carbon steel with a carbon content of 0.05% is subjected to a controlled rolling process. The steel sheet thus produced is then converted into a tubular shape. The tubular product is then subjected to a concealed arc weld, using a welding wire corresponding to the AWS standard EA3 with 0.1% C. 2.0% Mn and 0.5% Mo and a TiO ₂ and

⁽ Melted Schwcißflußmiltel (melt type flux) containing BiOi can be used together Binder is produced.) The mechanical properties of the in this way

The weld metal produced are shown in Table 11. Table II

Combination test sheet steel

very low-carbon Suhl »)

Normal carbon steel ")

welding wire

.Sweat Melt

0.1% C-2% Mn -0.5% Mo melt / flux agent

with TiO; -

0.1% C-2% Mn -0.5% Mo melting flux

with TiO ₂ -B ₂ Oj

·) Steel with 0.05 C-03 Si-1.5 Mn-0.2 NiO. 25 Mo-0.05 Nb-0.07 V-O.OJ Al-0.01 Ti * ') Steel with 0.09 C-0.3 Si-1.6 Mn-0.3 Cu-0.3 Ni-0.05 Nb-0.09 V-0.03 Al

Charpy impact test results with
2 mm VK inheritance

60 attempts
Mean value 18.1 kgm
Fluctuation range ff = 3.5

60 attempts.
Mean value 20.5 kg m
Fluctuation range σ = 0.9

The tests carried out show a reduction in the high-temperature ductility of the weld metal and a tendency for defects to form in the weld metal. As a result, as can be seen from Table II, the fluctuation range of the low-temperature toughness is greater than in the weld metal of a steel with normal Carbon content.

On the other hand, with a conventional low-alloy steel with 0.09% C, that with the above mentioned concealed arc welding process was welded, no reduction in high-temperature toughness. The range of fluctuation in the low-temperature toughness is also small, as can be seen from Table II. The problem that occurs when welding a very low carbon steel with the weld metal The lack of breaking strength seems to be a consequence of the combination of a welding wire with the usual one Carbon content and a very low carbon steel.

The invention is based on the object of a concealed arc welding method according to the preamble of claim 1 to provide, in which both good high-temperature ductility and good The low-temperature toughness of the weld metal is guaranteed.

This object is achieved with the characterizing features of claim I. The solution to the task is based on the surprising finding that a suitable combination of a very low carbon Steel with a welding wire and a welding flux of the specified composition the above Properties of the weld metal can be achieved. It turns out that the problem of reduction the high-temperature ductility of the weld metal is closely linked to the carbon and boron content of the weld metal.

The invention is explained in more detail below with reference to the drawing. It shows

F i g. 1 is a schematic view of a simulation device for the heat cycle during weld solidification,

F i g. FIG. 2 is a graph of the ductility of various solidified metals at high temperatures compared with the The simulation device of FIG. 1 were determined,

F i g. 3 is a schematic view of the sample position of a sample in the simulation device of FIG. 1,

4 shows a schematic view of the sample position of a sample in the Charpy impact test (notched impact test), and

F i g. 5 is a view of the joint geometry of the plates (electrodes) used in the examples of the invention.

F i g. 1 is a schematic view of the simulation device used for the heat cycle in weld solidification. The device has an infrared thermometer A, a pressure cylinder ß with an air-operated pressure accumulator, a (force) -measuring cell C, a dilatometer (strain gauge D), a chamber E, a sample F, an induction coil G and two water-cooled copper blocks. A detailed explanation of this simulation device is given in "A Mechanism of High Temperature Cracking in Steel Weld Metals", Welding Journal, Vol. 58, September 1979, pp. 277 ff.

The diagram of FIG. FIG. 2 shows the results of FIG. 2 with the simulation device of FIG. 1 carried out Attempts in which the temperature dependence of the ductility of various metals immediately after their Solidification is shown.

3 shows the UP weld metal 12 of an examined round rod 11 with a diameter of 10 mm. The chemical Composition of weld metal 12 of eight samples examined is shown in Table III.

The solidified metals designated by the numbers 1 to 8 in Fig. 2 have the same chemical Composition as those of Table III and / or their high temperature ductility. The shares are each expressed in percent by weight.

1) 1 Si Mn 31 P. 38 084 Mon Ti B. vE-50 Tabel C. (kgm) No. 0.26 1.62 0.018 S. 0.13 0.1 2.8 0.03 0.27 1.58 0.019 0.12 0.02 0.0045 6.7 1 0.03 0.27 1.63 0.017 0.015 - 0.01 0.0051 12.2 2 0.06 0.26 1.58 0.015 0.012 - - - 2.5 3 0.07 0.25 1.59 0.016 0.017 - 0.02 0.0039 12.0 4th 0.07 0.31 1.60 0.017 0.016 0.12 0.01 - 3.2 5 0.12 0.29 1.58 0.015 0.013 0.12 0.02 0.0044 10.5 6th 0.13 0.30 1.64 0.015 0.012 0.12 0.02 0.0047 7.8 7th 0.14 0.015 8th 0.013

The test section of the welding rod 12 (Fig. 3) is approximately 6 mm wide and is heated, melted and cooled in a thermal circuit which simulates that of submerged arc welding. During the cooling process, the test section is broken by an external force. The ductility at the time of fracture is usually represented by the reduction in the fracture area in% ((partial area during solidification - partial area after fracture / partial area during solidification) x 100). If the reduction in surface area between 1300 and 1000 ⁰ C maintains a value of more than 50% after it suddenly rises from zero at the solidification point, there is no risk of a defect even if a transition deformation can occur, as is the case with pipe production by welding.

The high temperature ductility of the weld metal of a low alloy steel can be known can be improved by reducing the carbon content of the steel. This is in accordance with F i g. 2, which shows that the steel containing no boron has good high temperature ductility is reached when the carbon content decreases below a certain limit.

On the other hand, this does not apply to the weld metal of a steel that contains boron. F i g. 2 shows that the high temperature ductility of a boron-containing steel decreases sharply even if the carbon content is between 0.06 and 0.14%. This is examined in more detail below.

Among the systems No. 1,4 and 6, which contain no boron at all, the system No. 6 with 0.1% C shows a relatively low ductility value. Nevertheless, the ductility of the steel of system no. 6 remains greater than 50% at all temperatures between 1300 ⁰ C and 1000 ° C, so that there is a defect even at high strain no danger.

In the case of the steel from system no. 2, which like that of system no. 1 contains 0.03% C, but also 0.0045% B, the ductility increases only slightly below the solidification point and, moreover, remains extraordinary ^{at all temperatures below 1300 ° C.} low, namely below about 30%. A similar tendency can be observed in system no. 3 with 0.06% C and 0.0051% B. If the solidified metals No. 2 and 3 are severely deformed, a defect, in particular a crack, can occur in the bead bend test.

Steel no. 5 with 0.07% C and 0.0039% B has a slightly lower ductility than steel no. 4, the also 0.07% C. but does not contain boron. However, the No. 5 steel exhibits a rapid recovery in ductility immediately below the solidification point and beyond that a ductility of more than 80% at temperatures below 1300 ° C. There is thus no risk of defects occurring in this steel.

Although the # 7 steel with 0.13% C and 0.0044% B has a much lower ductility than the # 5 steel, its ductility at temperatures below 1300 ° C is about 70%, so that also no danger for There are defects.

Steel No. 8 with 0.14% C and 0.0047% B, like steels No. 2 and 3, exhibits poor ductility recovery below the solidification point. In addition, its ductility only reaches ^{50% in the vicinity of 1200 °} C. and is generally about 40% at temperatures below 1300 ^{° C.} This is why there is a risk of defects in this steel when it is subjected to high loads.

As shown in FIG. 4, the specimens 13 were subjected to a Charpy notched impact test, the examined specimen section being the same as in the simulation test for the heat cycle during weld solidification. The sample 13 for the Charpy impact test has a notch 14, and the experiment was carried out at - 50 ⁰ C performed. The results are given in Table III.

From the comparison of steels No. 3.5 and 7 with good low-temperature toughness with steels No. 4 and 6 with poor low-temperature toughness, it is understood that there is satisfactory low-temperature toughness can only be achieved in the presence of both Ti and B.

A comparison of steel no. 2 with steel no. 3, 5 and 7 also shows that in The presence of Ti and B cannot achieve satisfactory low temperature toughness if the The carbon content of the melt is extremely low.

On the other hand, the low-temperature toughness is also poor when the carbon content is used as in steel No. exceeds 8.0.14%.

The above test results represent the starting point for the invention. The very low Carbon steel to which the method according to the invention is applied is a low-alloy, high-strength steel Steel that is suitable for conduit in cold climates.

Examples of the composition of such chairs are given below (proportions in percent by weight):

No. C. Si Mn P. S. Cr Ni Mon Nb V Ti B. A.
B. 0.049
0.021 0.29
0.14 1.56
1.59 0.017
0.018 0.005
0.003 0.01 0.27 0.25 0.049
0.041 0.068 0.007
0.017 0.0010

When welding a steel with 0.005 to 0.06% C z. B. with the UP welding process should the welding wire contain more than 0.18 to 0.55% C. The reason for this is that to achieve more satisfactory High temperature ductility with a view to preventing defects in a weld metal containing boron, the carbon content of the weld metal must be in the range between 0.07 and 0.13%. With submerged arc welding of a steel with 0.005% carbon, the carbon content of the weld metal falls in the specified is Range if the welding wire contains 0.3ö to 0.55% C. On the other hand, it sinks when submerged steel is welded with 0.06% C the carbon content of the weld metal in the range mentioned when the welding wire is over Contains 0.18 to 0.33% C.

Based on the above considerations, the carbon content of the welding wire for the Submerged arc welding of a steel with 0.005 to 0.6% C in the range from over 0.18 to 0.55%. If the If the carbon content is in the above range, the low-temperature toughness of the molten material will also be greatly improved.

It is of the utmost importance that the welding wire and / or welding flux be titanium and / or boron contains so that the weld deposit contains both titanium and boron.

In the presence of boron, titanium makes the microstructure of the steel much finer and thus improves it Low temperature toughness. To prevent fluctuations in the low-temperature toughness and good To achieve low-temperature toughness, both B and Ti must be present in the weld gui, which means that it can be achieved that in each case at least one of the two elements in the welding wire and / or in the weld nut means is included.

The proportion of Ti and B present in the weld metal should be in the range from 0.004 to 0.035% Ti and 0.001 to 0.005% B.

If the total amount of Ti in the weld metal is less than 0.004%, the low-temperature toughness cannot be satisfactory to be achieved; if this proportion exceeds 0.035%, the toughness of the reheated becomes or reheated weld metal deteriorated.

If Ti is added to the weld metal from a solid welding wire and is contained in the welding wire, it should be present as an alloying element with a proportion of 0.004 to 0.035 percent by weight. When a If welding wire with a flux core is used, Ti is added in the form of ferrotitanium.

When Ti is added from the welding flux, it can be considered rutile. Titanium slag or ferrotitanium can be added. If Ti is added from the welding flux in the form of rutile, titanium slag or ferro-titanium, the addition of 5 to 30% in the form of TiO ₂ or 0.5 to 5% in the form of ferro-titanium (50% Ti) corresponds to the addition of 0.004 to 0.035 % Ti to the weld metal.

If the total amount of B contained in the weld metal is less than 0.001%, it cannot be sufficient Low-temperature toughness can be achieved while a proportion higher than 0.005% because of the greater susceptibility is undesirable for high temperature cracks.

When boron is added of a solid (solid) welding wire, it should preferably ⁴ ^ present in the welding wire as an alloying element in a proportion in the range of 0.002 to 0.01%. When using a welding wire with a flux core, B can be added as an alloy element in the form of ferroboron. Boron can also be added from the welding flux in the form of boric acid, a borate or a boron-containing alkali metal salt such as borax or ferroboron.

If boron from the welding flux is added in the form of boric acid, a borate, borax or ferroboron, the addition corresponds to 0.05 to 1.0% in the form of B ₂ 01 or 0.07 to 1.7% in the form of ferroboron (20% B) the addition of 0.001 to 0.005% B to the weld metal.

With regard to compounds such as rutile, titanium slag, boric acid, borates, borax, etc. can be through use the same effect can be obtained from either bound or molten flux.

The welding wire used preferably contains 0.01 to 0.5% Si and 0 to 3.5% Mn as main components. Silicon in the welding wire acts as a reducing agent. However, if the silicon content exceeds 0.5%, the resistance of the weld metal to cracking is reduced. On the other hand, no satisfactory reducing effect is obtained if the silicon content is less than 0.01%

An addition of manganese creates a needle-shaped ferritic microstructure (fine structure) in the weld metal, whereby the low temperature toughness is improved. If the manganese content is less than 0.9%, none can sufficient low-temperature toughness can be achieved. If the manganese content exceeds 3.5%, the low-temperature toughness will decrease also deteriorates and, moreover, the drawability of the wire decreases.

Only the carbon content of the entire welding wire must be within the specified range; the welding wire used according to the invention can have any desired shape and can in particular be either a solid wire or a wire with a flux core, which is made from a wire tube into which a metal or an alloy powder is introduced which comprises part of the alloy composition
In addition to the above elements, the welding wire used can contain less than about 0.6%

10

20th 25th 30th 35

Mo and / or less than about 3.5% Ni can be added.

An addition of up to 0.6% Mo improves the strength of the weld metal. If the molybdenum content, however Exceeds 0.6%, the low-temperature toughness is significantly deteriorated. A proportion of up to 3.5% Ni improves also the low-temperature toughness. However, if more than 3.5% Ni is added, the Low-temperature toughness decreases noticeably.

As explained above, according to the invention, by limiting the carbon content of the weld metal to 0.07 to 0.13%, the reduction in the high-temperature ductility of the weld metal due to the Boron content can be prevented. If therefore the welding process using multiple electrodes is carried out, all welding wires need not necessarily have the composition given above exhibit. According to the invention, conventional welding wires can also be used together with welding wires and thickening fluxes having the specified composition of the present invention can be used.

The welding can be carried out satisfactorily if the basicity of the welding flux used between 0.5 and 2.5 according to the marking of the UW (International Institute of Welding). The basicity is determined according to the following formula:

Basicity

CaO,% + MgO,% + BaO,% + CaF ₂ ,% + - (MnO,% + FeO,%)
SiO ₂ ,% + j (Al ₂ Oj,% + TiO ₂ ,%)

When the basicity is less than 0.5, the oxygen content in the weld metal increases extremely and if the basicity is larger than 2.5, the low-temperature toughness deteriorates. is hardly a good machinability of the weld metal.

The advantages are explained in more detail below using the examples:

Tables IVa and IVb show the chemical compositions of welding wires, fluxes and Steel sheets together with the respective welding conditions.

In Tables IVa and IVb, A, C, E, G, M, N, O, P. Q and R are comparative examples, while B, D, F. H, I, J, K and L are examples of welding wire and flux compositions. The specimens for the notched impact test According to Charpy, each welded joint was based on the one shown in FIG. 4 taken from the manner shown, and the samples for the longitudinal bead bend test were taken from the taken from the same area.

Table IVa

No.

Chemical composition of the Schwuißdraht (wt .-%) C Si Mn Mo Ni Ti

Arid wire

Wire 0 (mm)

A. 15th F. 0.60 0.55 2.04 - - - - solid 4.0 , 0 B 0.19 0.11 1.97 _ - - - solid 4.0 C. 0.09 0.03 1.98 0.25 0.01 0.22 - solid 4.8 D. G 0.21 0.09 2.52 0.23 - 0.23 - solid 4.8 E. 50 H. 0.11 0.15 3.6 0.25 - - 0.006 with 4.8 J Flux i core") K 0.27 0.12 2.02 0.43 - 0.12 0.006 with 4.8 L. Flux 55 M. core") N 0.15 0.08 1.42 0.52 0.05 0.31 - solid 4.8 O 0.26 0.15 1.58 0.19 - - - solid 4.8 P. 0, ¹ 9 0.02 1.08 - 1.40 0.05 _ solid 4.8 Q 0.51 0.15 1.03 0.01 - 0.03 - solid 4.8 bO R 0.21 0.05 2.05 - - 0.15 0.004 solid 4.0 0.27 0.12 2.10 0.25 - - 0.003 solid 4.0 0.26 0.15 1.58 0.19 - - - solid 4.8 0.26 0.15 1.58 0.19 - - - solid 4.8 0.19 023 1.65 0.20 - - - solid 4.8 031 0.14 1.49 - - - - solid 4.8 0.26 0.15 1.58 _ - - - solid 4.8 0.26 0.15 1.58 - - - _ solid 4.8

65

Table IVa (continued)

No. Chemical composition of the llulimitlels ((jcw .-%) Al ₂ O, TiO ₂ CuO MgO IkO CaI-, C Si Mn Nb V other BjO ₁ Biisi- Andes Particle I. IO SiO ₂ Fabrics / itiäi Flux size I. 17.7 24.2 4.9 24.6 14.0 0.05 0.32 1.54 0.04 0.05 0.7 1.30 (mesh) A. 12.5 17.7 24.2 4.9 _ 24.6 14.0 0.05 0.32 1.54 0.04 0.05 - 0.7 1.30 melted 40 χ 250 B. 12.5 38.2-15.8 _ - 29.9 0.05 0.32 1.54 0.04 0.05 _ 0.3 1.34 melted 40 χ 250 I. C. 14.9 38.2-15.8 - - 29.9 0.05 0.32 1.54 0.04 0.05 - 0.3 1.34 melted 20 χ 250 D. 14.9 28.3 19.0 4.9 - 10.4 14.3 0.025 0.14 1.91 0.0t> - MnO 0.85 melted 20 χ 250 E. 17.4 5.3 melted 20 χ 250 28.3 19.0 4.9 ■ - 10.4 14.3 0.025 0.14 i, 91 Ü.Oö - MnO 0.85 20th F. 17.4 5.3 melted 20 χ 250 13.2! 6.8 10.5 34.6 - • 0.0 0.025 0.14 1.91 0.06 - Na ₂ O 0.5 2.25 G 10.5 2.2 bound 12x100 13.2 16.8 10.5 34.6 - 10.0 0.025 0.14 1.91 0.06 - Na ₂ O 0.5 2.25 25th H 10.5 2.2 bound 12x100 28.2 19.1 4.8 - 10.2 14.6 0.05 0.38 1.28 0.03 0.03 MnO 0.7 0.83 1 14.9 5.3 melted 20 χ 250 60.2 - 8.8 8.9 - 8.7 0.008 030 1.95 0.06 - - 0.2 0.62 J 12.5 28.2 19.1 4.8 - 10.2 14.6 MnO 0.2 0.83 melted 20x250 JO K 14.9 28.2 19.1 4.8 10.2 14.6 0.05 0.38 1.28 0.03 0.03 3, J
MnO 0.83 melted 20 χ 250 L. 14.9 5.3 melted 20 χ 250 6.2 16.8 15.2 1.4 _ 3.5 0.025 0.14 ! .91 0.06 - MnO 0.3 0.47 M. 14.4 12.2 melted 40 χ 250 19.0 0.6 13.2 27.2 - 26.1 0.025 0.14 1.91 0.06 - MnO 0.3 3.11 35 N 12.8 0.8 melted 40 χ 250 13.2 16.8 10.5 34.6 - 10.0 0.025 0.14 1.91 0.06 Na ₂ O 0.5 2.25 O 10.5 2.2 bound 12x 100 40 13.2 16.8 10.5 34.6 - 10.0 Na ₂ O 0.5 2.25 P. 10.5 2.2 bound 12x100 28.2 19.1 4.8 - 10.2 14.6 MnO 0.83 45 Q 14.9 5.3 melted 20 χ 250 60.2-8.8 8.9 - 8.7 - 0.3 0.62 R. 12.5 melted 20 χ 250 Table IVb Chemical composition of the steel sheet (weight - ^ö / i>) No. thickness Al Ti Combina 50 (mm) Mo other tion *) 25.0 0.019 0.014 elements A. 25.0 0.019 0.014 0.20 - 1 B. 19.5 0.019 0.014 0.20 - I. C. 19.5 0.019 0.014 0.20 Il 55 D. 19.5 0.020 0.019 0.20 - II E. - B. III mc 0.020 0.0 i 9 0.0012 Γ
ι - B. iii 19.5 0.020 0.019 0.0012 60 G - B. III 193 0.020 0.019 0.0012 H - B. III 193 0.03 0.010 0.0012 I. 0.10 Ni II 65 193 0.021 0, OiI 0.93 I. - B. II 193 0.03 0.010 0.0014 K 0.10 Ni Π 193 0.02 0.019 0.93 L. - B. III 19.5 0.020 0.019 0.0005 M. - B. III 193 0.020 0.019 0.0012 N G IU

continuation

No. Chemical composition of the steel sheet (% by weight) C. Si Mn Nb V Al Ti Mon other Combina thickness elements tion *) 5 (mm) 0.003 0.35 1.95 0.05 0.020 0.019 0.21 B. O 22nd 0.0008 1 0.09 0.24 1.56 0.05 0.07 0.022 0.015 0.10 - P. 22nd 0.018 0.16 2.01 0.05 - 0.015 0.018 030 B. 1 10 Q 19.5 0.0012 Ul 0.018 0.16 2.01 0.05 - 0.015 0.018 0.30 B. R. 19.5 0.0012 IH

Note on the tables:

*) Welding conditions: combination

No. 1,600 A x 35 V x 300 mm / min. Direct current. Single wire. Conclusion as in Fig. 5 shown,
with t = 25 mm. / 2 = 8 mm, (3 = 9 mm, tt = 8 mm θ \ = 90 ". Fy = 90".

No.

No. Ill

Front electrode Rear electrode

1100 A 35 V 900 A 40 V

1100 mm / min 1100 mm / min

Joint geometry as in FIG. 5 shown, with t] = 19.5 mm, / 2 = 7 mm. fj «■ b mm. u

Front electrode Middle electrode Rear electrode

1350 Λ · 35 V ■ 1200 mm / min

1000 Λ · 40 V ■ 1200 mm / min

780 Λ 38 V ■ 1200 mm / min

Alternating current, double wire

ι = 70 °. 6I ₂ = 90 ". Weehclstrom. Triple-electrode wire

Joint geometry as in FIG. 5 shown, with i | = 19.5 mm. /> ■ = 7 mm, i | = h mm, r «

b.5mm.6> i = 70 ",

90 ".

**) The welding wires with fluffing cores contained 15% CaF _{2 in addition to the components listed in Tables E and F.}
Boron was added as ferroboron (20% B).

The test results are shown in Table 5.

When welding wire is used with the composition, the proportions of C, Ti and B are im Weld metal 0.07 to 0.13% C. 0.004 to 0.035% Ti and 0.001 to 0.005% B. As from Table V for samples B, D, F, H, I, J, K and L can be seen, the weld metal does not crack in the bending test, and it does satisfactory vE value achieved at -60 ° C.

On the other hand, if a conventional welding wire or a welding wire larger than that Finally, when carbon content is used, the carbon content is less than 0.06% or more than 0.20%, which leads to the appearance of fine cracks in the bending test. In this case the vE value be also decreases -60 ° C occasionally below 3.0 kg m.

31 38 Ti B. 084 number of vE-60'C Comparison 10 Ü Table V 0.020 0.0052 Cracks *) (kg-m) example 1 No. Composition of the weld metal (%) Average/ invention H 0.019 0.0048 smallest word Comparison 30 I. 0.025 0.0024 19th 7.5 / 3.2 example C. invention 15th j A. 0.20 0.026 0.0022 0 16.4 / 15.9 Comparison 1 0.020 0.0019 4th 16.2 / 13.8 example 1 B. 0.080 invention 35 I. C. 0.060 0.018 0.0018 0 18.5 / 16.3 Comparison 0.037 0.0038 26th 6.8 / 2.9 example 20th D. 0.087 invention E. 0.041 0.020 0.0036 0 12.4 / 11.3 invention 0.022 0.0045 8th 4.2 / 2.8 invention F. 0.078 0.005 0.0021 invention G 0.052 0.032 0.0028 0 9.5 / 8.2 invention 0.017 0.0013 0 14.8 / 13.3 Comparative H 0.077 0.012 0.0023 0 10.5 / 8.8 example 1 0.075 0 13.2 / 12.0 Comparison j 0.13 0.020 0.0025 0 11.8 / 10.5 example K. 0.081 0 3.2 / 2.3 Comparison L. 0.075 0.028 0.0032 example M. 0.070 3 ") 9.8 / 8.2 Comparison 0.025 0.0033 example N 0.076 12th 6.5 / 2.8 Comparison 0.026 0.0008 example O 0.045 U 8.8 / 5.3 Comparison 0.002 0.0022 example P. 0.14 0 4.5 / 2.7 Q 0.072 0 3.9 / 2.1 R. 0.073 25th

*) Number of cracks in the Elicgcversuch.
**) Cracks caused by slag infiltration.

For this purpose 2 sheets of drawings

Claims (7)

Patent claims: 1. Concealed arc welding process for low carbon steel containing 0.005% to 0.06% carbon, especially for the production of line pipes, using a carbon containing- 5 the welding wire, titanium and boron being added to the weld metal, characterized in that that the welding wire contains from 0.18% to 0.55% carbon. 2. The method according to claim 1, characterized in that titanium and boron for welding wire and / or added to the welding flux. 3. The method according to claim 1 or 2, characterized in that the welding flux rutile and / or ίο titanium slag in a proportion of 5 to 30% (as TiO ₂ ) and boric acid, a borate and / or ferroboron in a proportion of 0.05 contain up to 1.0% (as B ₃ Oj). 4. The method according to claim 1 or 2, characterized in that the welding flux ferrotitanium in a proportion of 0.5 to 5% (as Fe-Ti alloy with 50% Ti) and ferroboron in a proportion of 0.07 to 1.7% (as Fe-B alloy with 20% B) 15th 5. The method according to claim 1 or 2, characterized in that the welding flux 5 to 30% TiO ₂ or 03 to 5% ferrotitanium (ah Fe-Ti alloy with 50% Ti) and boric acid, a borate or boron with a proportion of 0.05 to 1.0% (as B ₂ O ₃ ) or 0.07 to 1 , 7% ferroboron (as Fe-B alloy with 20% B). 6. The method according to any one of claims 1 to 5, characterized in that the welding wire 0.004 to Contains 0.035% Ti and 0.002 to 0.010% B. 20th 7. The method according to any one of claims 1 to 6, characterized in that the welding flux a Has basicity from 0.5 to 2.5.